This type of valve is commonly employed in cooling circuits associated with heat engines having large cubic capacities, especially those with which trucks or some motor vehicles are equipped, in a case of which cooling fluid flow rates necessary for their operation are higher than those encountered in a case of heat engines having smaller cubic capacities, for which thermostatic valves generally have a flap.
FIG. 1 shows a known valve 1 of that type, distributed under reference “DB 54” by the company VERNET (France), which comprises a casing 2 delimiting a fluid inlet 2A and two fluid outlets 2B and 2C. The valve is, for example, incorporated in a cooling circuit in such a manner that the inlet 2A is supplied with a cooling fluid coming from an engine, the outlet 2B is connected to a path for direct return of the fluid to the engine, and the outlet 2C is connected to a return path extending through a heat exchange radiator. In order to regulate passage of the fluid between the inlet and one and/or the other of the outlets, the valve 1 is provided with a tubular sleeve 3, of which base 3A is open, a skirt 3B is solid and a free rim 3C is flared in a shape of a flat annular disc. The skirt 3 is guided by a seal J in an opening which separates passages 2B and 2C.
The rim 3C is suitable for coming into sealing contact with a seat 4 which is fixedly joined to the casing in such a manner that, when the sleeve is supported against the seat, fluid entering the valve by way of the inlet 2A is directed, inside the sleeve, as far as the outlet 2B and, when the sleeve is moved away from its seat, at least some of this incoming fluid is diverted around the sleeve in order to be evacuated from the valve by way of the outlet 2C.
Displacements of the sleeve 3 relative to the seat 4 are controlled by a thermostatic member 5 whose body 5A is located in a flow path of the fluid, at a location of the inlet 2A, and whose piston 5B abuts an end piece 9A which is itself fixedly joined to the base 3A of the sleeve. When a temperature of fluid in which the body 5A is immersed increases, expandable wax contained by that body brings about displacement of the piston 5B and a driving of the sleeve. A spring 6 is interposed between a stirrup 9B which is fixedly joined to the end piece 9A, and therefore to the sleeve 3, and a support member 7 which is fixedly joined to the body of the thermostatic member in order to return the sleeve to its seat when the temperature of the fluid decreases.
It will be appreciated that, when a temperature of incoming fluid is very high, displacement of the sleeve 3 is such that it abuts a wall 2D of the casing 2, which wall is located in a path of the sleeve. In order to prevent damage to the wall and/or the thermostatic member 5, it is provided that the body 5A of the thermostatic member is not connected rigidly to bridges 4A of the seat 4 but is positioned by these bridges while preserving freedom of displacement in a direction of displacement of the piston. Thus, when the sleeve comes into abutment with the wall 2D, the piston is immobilized relative to the casing, and the body 5A moves away from the piston (towards the right in FIG. 1). In order to return the body 5A and keep constituents of the valve at rest, an over-travel spring 8 is provided between the support member 7 and the bridges 4A of the seat 4.
Although the valve described above is satisfactory, it nevertheless has a disadvantage of being impossible to regulate once assembled and incorporated in a cooling circuit because a temperature at which the sleeve starts to move away from its seat, and a degree of opening of a passage between the inlet 2A and the outlet 2C, are predetermined by the thermostatic member used. That disadvantage is even more marked when it is desired to design a cooling circuit for a vehicle which is to travel under varied operating conditions, in particular in accordance with a speed of the vehicle and/or a load drawn by that vehicle.